Timestamp masking is a data augmentation and regularization technique in time series machine learning where specific time steps or their latent feature representations within a temporal sequence are randomly hidden or set to zero during training. By altering the context while preserving overall sequence alignment, this technique generates diverse views that encourage neural networks to infer missing information from surrounding observations and learn robust temporal dependencies. It is commonly applied in self-supervised and contrastive learning frameworks to prevent overfitting to raw observation values and to facilitate fine-grained representation learning for downstream tasks such as forecasting, classification, and anomaly detection.